The present invention relates to a sample introduction assembly for loading samples into analytical crucibles for subsequent fusion and analysis.
An analytical furnace employs relatively small pin, chip, or other samples, typically in sizes of from about 1 mg to about 1 g. Graphite crucibles are employed for resistance heating of a crucible directly when placed between a pair of electrodes. Ceramic crucibles are employed in furnaces in which heating is by an induction field provided by an RF coil. In either furnace, it is necessary initially to outgas the crucible and assure no contaminant gases are mixed with the specimen gases during loading of the sample.
In several prior art systems, it is necessary to open the combustion chamber area after the outgassing to gain access to a crucible for insertion of a sample to be analyzed. In doing so, the crucible is exposed to atmospheric gases which can contaminate the crucible to an extent that the analytical results can be adversely effected. In order to prevent the introduction of contaminants, one solution has been to provide a sample loading mechanism which allows the introduction of a sample into a movable hopper which is subsequently sealed and the area purged with an inert gas. The jaws of the hopper are subsequently opened to allow admission of the sample into the crucible through an electrode assembly in resistance furnaces. U.S. Pat. No. 4,371,971 discloses such an apparatus. Although preventing a direct communication path with the atmosphere during admission of the sample, it may still allow a small amount of atmospheric gases to enter the combustion chamber during the sample loading operation. Improved sample loading mechanisms have been designed for introducing samples into a crucible while minimizing the introduction of contaminants into the furnace. U.S. Pat. No. 6,291,802 discloses one such system. U.S. Pat. No. 7,402,280 also discloses a crucible and sample loading system in which a plurality of samples are mounted in stacked carousels and are selectively transported from the carousel to the analytical furnace.
In order to automate the successive analysis of multiple samples, a horizontally extending sample holding carousel has also been employed and positioned above the sample drop assembly to introduce samples into the sample drop assembly shown, for example, in the above '802 patent. In such system, the sample holding carousel is positioned above the furnace, however, it is somewhat difficult for an operator to load the carousel while mounted to the furnace without the use of a step stool or other means for elevating the operator. There remains a need, therefore, for an improved sample handling apparatus which is easier to use and preferably one which can contain multiple samples for successive automatic introduction of samples into a combustion furnace for analysis.